Want to start reading crime novels, but the vocab wall looks hard to scale? Welcome in.
I’ll preface this by saying I am not an expert on the Japanese legal system. I am a fan of crime novels, mysteries, and police procedurals. I enjoy introducing other people to these genres, but have found the hurdle of vocabulary to be high for some people’s tastes. There are also likely substantial differences between how the Japanese justice system works and your own. I try to cover what I know of that below, but please remember: fiction is an imperfect mirror to reality. While laws and customs of Japan will of course be present and influential in the books you read, crime novels and police procedurals have tropes, reader expectations, and author whimsy driving them in ways that force divergences from reality.
With that out of the way, this post will be in several sections with relevant vocabulary groupings and longer form notes at the bottom. It’s not comprehensive - these were words I can up with off the top of my head or by searching my anki deck. But if you’re looking to get into Japanese crime novels, or just curious about the sorts of things you’d come across in them, this is a start.
Basic vocab (for beginners)
警察 police
警官 police officer
刑事 detective
検察庁 public prosector’s office
逮捕 arrest
手口 - modus operandi (how they did it, it being the criminal act)
手錠 handcuffs
自殺 - suicide
殺人・殺人犯・殺人鬼 - murderer
他殺 - murder
刑務所 prison
勾留 - detention pending trial / “in custody”
拘置所 - jail
自首 - surrender / turn oneself in
自白 - confess
脱出 - escape
凶器 - weapon
動機 - motive
検挙 - arrest
事情聴取 - often just called 聴取; questioning (of a person, eg, witness or suspect)
死体 - corpse
遺体 - corpse, but polite
死骸 - corpse, but impolite
霊安室 - morgue
変死体 - suspicious death (it looks like it means weird corpse, I know, but it’s used in the same fashion English cop shows would use ‘suspicious death’ so that’s what I’m putting it as)
泥酔 - blackout drunk. Not specifically a crime/cop word but seems to come up more in crime media due to 泥酔状態 being an easy state to take advantage of
検死 - autopsy (specifically think of this like specifying a coroner’s inquest vs a generic autopsy)
解剖 - autopsy
窃盗 - theft, larceny
盗撮 - filming or photography without consent. If not specified further in the source material, assume upskirt photos of women.
防犯カメラ - surveillance camera
裁判 - trial
裁判官 - judge
法廷 - court
審理 - trial
捜査 - investigation
行方不明 - gone missing; whereabouts unknown
失踪者 - missing person (行方不明者 is also said, but I feel this one is more common)
陰謀 - plot, scheme
官舎 - living quarters provided for police. Has cheaper rent, common for lower ranks to live in, and I think even higher ranks, but it’s not compulsory. That said, googling around it seems officers are certainly encouraged to live there.
手帳 - technically ‘notebook’ but in context here it’s police badge/identification. You’ll see this used similarly in 生徒手帳 for student IDs
Slang and/or 専門用語
マル「x」- there’s a lot of things that are shorted to maru-whatever. The maru here is actually 
so far as I know. The ones I know are マル暴(criminal, specific to organized crime. From 暴力犯)、マル被 (suspect, from 被疑者)、マル害 (victim, from 被害者)、マル対 (person you’re staking out or investigating)
Google tells me マル目 (eye witness, from 目撃者) is also a thing but I don’t think I’ve run across that one myself.
ピンハネ - taking a kickback
面割り= line up (for purposes of identification). Usually photos, I don’t think I’ve ever seen the ‘collect 5 guys in a room and identify which one’ trope in Japanese tv. If you’re used to seeing 面 in words like 仮面 it’ll probably be easier to remember this. Think ‘separating faces’.
ホシ = criminal. Apperantly this comes from「目星をつける」
ヤマ = case; 事件
地取り = think of this like 地域＋聞き取り. It’s basically going around and talking to people in the area
逆探知 - phone tracing
任同＝任意同行=voluntarily going in for questioning
ハム = 公安警察 (public safety) for the hilarious reason that 公 looks kinda like ハム
フダ＝逮捕状 (arrest warrent). Think of this as 札 and it will probably feel more clear
前足・後足 = before and after the crime. Basically, what was the criminal doing before/after. Think like following footsteps
マトリ = 麻薬取締部. Another abbreviation. They deal with drug offenses (if that’s not obvious from the long name)
アジト = hiding place. I think this is a loan word from some language not English. Russian?
デカ = detective
ウサギ = criminal on the run
オレオレ詐欺 = crime targetting old people by phone via pretending to be a relative in distress
パクる = arrest
アヒル = uniformed police officer. I think this one is a bit derogatory
お巡りさん - uniformed police officer, but a nicer term and one you’ll hear regular people use when addressing police (not to be used with detectives)
夜廻・夜回り - night watch/night shift
縄張り - turf (think gangs)
死亡推定時間 - estimated time of death
サツ - 警察
特ダネ - exclusive scoop (journalism, which crosses streams with police procedurals a lot)
ネタ - scoop or lead (journalism)
シロ・クロ = not guilty/guilty. You’ll hear suspects referred to as ‘black’ or ‘white’ - black meaning guilty and white being not guilty.
落とす - literally ‘to drop’ this means ‘to confess’. The title of 半落とし refrerences this because the person who confesses at the beginning of the book only “half confesses”. Often this is used in the sense of 'getting someone to confess’
洗い出す - basically ‘investigate’ or ‘go ask some questions’
ゴタ = kinda general slang; if you know ゴタゴタ this one shouldn’t be hard to guess but it’s basically just ‘trouble/problems’
調書 - “A public document drawn up by a court or investigative authority to certify the course and details of a case, in accordance with procedural law” (English single word definitions are things like ‘written evidence’ which I feel is a bit unhelpful)
霞ヶ関 - this is actually a place, but it comes up sometimes because it’s an area of Tokyo with most of the government ministry offices are located
押送 - transferring a convict from prison to somewhere else (under guard)
Legal terms
婿養子 - adopted son in law. This comes up a lot due to inheritance and such
箝口令 - gag order
控訴 - appeal
被告 - the accused
器物損壊 - property damage (not including ships, buildings, planes and documents)
再審請求 - petition for retrial
公務執行妨害 - interference with a public servant in the execution of his or her duties
起訴 - indictment
起訴猶予 - suspension of indictment
求刑 - recommended sentence
時効 - statute of limitations
私的制裁 - vigilantism
公然猥褻罪 - public indecent
服役 - serving time in prison
立件 - assembling a criminal case
嘱託殺人 - murder of someone who asked to be killed, “consensual homicide”
釈放 - release (from prison)
仮釈放 - parole
Forms of death
撲殺 - beaten to death
毒殺 - death by poisoning
溺死 - death by drowning
投身自殺 - death by jumping (out a window, etc)
即死 - sudden death. Usually used in the context of ‘it was painless’
餓死 - death from starvation
轢死 - death by being run over
焼死 - death by burning
窒息死 - death by suffocation
殉職 - being killed in the line of duty
他界 - 'passed on’; oblique phrasing. You’ll mostly see/hear it in reference to people who did not die from a crime
Forms of harm
打撲 - blow (could be punch or kick)
打撲傷 - bruise
毒薬 - poison
銃 - gun
機関銃 - machine gun
刃物 - sharp object (not necessarily a knife)
縄 - rope
飢え死 - starvation
絞殺 - strangulation
労災 - on the job injury/death/etc
Older, more archaic words
牢獄 - prison, “gaol”
捕縛 - arrest someone via tying them up with rope (google image search this)
Words more commonly found in formal writing
急逝 - same meaning as 即死 but more formal
享年 - one’s age at death (also: 没年)
Death practices
葬式 - funeral
葬儀 - funeral
遺影 - picture of the deceased (used during funeral service or placed in the home in a place of remembrance)
火葬 - cremation
土葬 - burial
三回忌 - second anniversary of a death
供養 - memorial serivice
線香 - incense
仏壇 - Buddhist household alter
Various notes ranks and teams
Police ranks are a bit tricky and they’re really important to understand for power plays. I don’t know the English name for some of these ranks because all that matters is that I know how they rank.
Remember that 巡査 is the lowest - entry level. Then you start climbing. 巡査部長 
警部補 警視 警視正 警視長 警視監 警視総監
検察官 are public prosecutors and they are comprised of multiple ranks. Starting from the bottom and going up: 副検事 検事 検事長 長次長検事 検事総
You aren’t aren’t キャリア until you hit 警部補. キャリア matters because in crime books there’s often tension between the キャリア組 and those who are not. Also it’s possible to be both, say, 警部補 and 係長 at the same time. This is because 警部補 is your rank and 係長 is your job title. So maybe you’re like the rank of 警部補 but your job title is 窃盗課係長.
You’ll see a lot of numbered 課s. Basically 1 = violent crimes, 2 = white collar financial crimes, 3 = theft, 4 = organized crime
You also have 鑑識課 (forensics, which includes 科捜研 which is more or less ‘the lab’) and 機捜 = a shortening of 機動捜査隊 or mobile police unit.
Further is is the 公安警察 who deal with things like extremist groups and political threats.
It doesn’t end with the 課s either, there are special groups like:
SIT = Special Investigation Team. Focus on kidnapping and hostage type stuff so very common in action packed crime media. You might also hear them referred to as 特殊班
サンザイ = financial crimes. Money laundering, kickbacks, embezzlement, etc. I think this derives from 散財
科捜研 = forensics. You’ll hear people talking about sending things to this team. It’s the lab, basically
General notes on the Japanese justice system
You may have heard the Japanese courts have a 99% conviction rate. This is true, but also different than it seems at first glance. You do not have a 99% chance of going to jail if you are arrested, you have a 99% chance of going to jail if they decide to prosecute. At the time of this writing, I see sources saying Japanese prosecutors defer 60% of the cases they receive (source). Prosecutors won’t pursue a case they don’t think they can win, which also drives the dynamics of these novels as you’ll see prosecutors kicking back a case to the police because they don’t think they have enough to convict.
There was also a change in the justice system introduced in 2009, 裁判員制度, called either ‘citizen judge system’ or ‘lay judge system’ or ‘quasi-jury system’ depending on which translation you use. This has changed the conviction rates somewhat and also how cases will play out. Because this is a relatively recent change, it’s worth noting what year your book was published if you’re reading about a trial.
It’s also important to call out that the Japanese police can hold you in detention, from a single arrest, for up to 23 days. Enjoy this PDF from the Australian Embassy in Japan which explains the process well. I will note that I’ve seen at least one book talk about immediately re-arresting someone for a different crime in order to hold them for longer, but I have no idea if that is legal or if instances of it have occurred.
In many books you’ll see references to ‘and they completely got away with it, since they were minors’. This is a bit complicated. While it is more or less true that juvenile crimes don’t go on your “permanent record” in the same sense as the west, some offenses can result in being tried as adult (if over 18, recall legal adulthood in Japan starts at 20) and kept into adulthood (although sometimes this doesn’t happen (source). An important distinction between juvenile and adult offenders is that juvenile offenders can not have their names reported in the press.
I’ll probably come back and edit this post if I find I’m missing something I think it dearly needs but, again, there’s no way I can be totally comprehensive. If you’re ever at a loss as to what a crime word means, especially if it seems to be slang, I highly recommend checking out 刑事弁護OASIS.
That’s really hilarious why this is ハム