When you choose this subclass you get:

 

3rd LvL:

Find the Culprit

You have 3 "? Tokens" up to 3 times a day you get a +1/+2/+4 to your perception and investigation rolls for 1min. Depending on how much Tokens you spend at once.
Recharges 2 Tokens up to 3 per 24h.

On Guard

When you choose this subclass you get following Wizards spells and cantrips Spells once per short/long Rest: Alarm, Animal Messenger, Arcane Lock, Light(might change)

Tells

You feel when people lie to you. You get Proficiency in Insight

                                                                                                                                                                                                                                                                                                              

7th LvL: 

Bad Cop

You are good at getting information. You get +1 to deception and intimidation.

Once per day you can try to daze your enemy with a blunt weapon. Forgo your attack action, to attack dealing 1d4+str and on a failed Con dc 12+STR: Inflicting disadvantage on Attack and Saving Throws until the end of the targets turn.(learned too late about new weapon abilities. Have to think about sth)

10th LvL:

Good Cop  

Your experience as a Investigator lets you uncover hidden clues and tells other people might miss when you interrogate someone.You get advantage on insight and intimidate rolls when questioning people.

15th LvL:

Freeze!

As a bonus action you can once per long rest try to intimidate your enemies in combat.  Designiate up to 2 Enemies if you intimidate them successfully their speed is reduced to 0 until the end of your next turn. They have to speak the same language as you, if they dont you get disadvantage on your intimidation roll.

(note not sure if i want to change Intimidate to just a DC 15 Wis / Con / Int Save) Since i like the Intimidation part to be more RP focused.)

 

18th LvL:

I Am The Law!

Other Security  Workers(for a lack of a better word) Respect you. You get Advantage on Persuasion rolls on other people in your line of work. Civilians wont call the guards for 1/d4 rounds if you are committing a crime in their vicinity.

Your Presence and Dedication Intimidates your foes. Enemies who suffered DMG from you get disadvantage on attack rolls against you until the start of your next turn.

I always liked Detective or Crime Stories. I like making plans in the game but always found Intelligence a lackluster stat for a fighter, who didnt wanna use magic abilities)
I learned that there is the Inqusitive Rouge after making this Subclass. But i find them not so much alike. The Inquisitve Rouge seems to be a more sneaky stealthy type. Who senses danger. But my Investigator is more like the rough cop from the 1800s, with a little more brain.

 

Find the culprit

X times a day you get a +1/+2/+3 to your perception and investigation rolls for 10min/1h(not sure if 1h is overkill)

They recharge at a long rest.

Bad Cop

You are good at getting information. You get +1 to deception and intimidation checks you get proficiency in intimidation

Once per day you can try to daze your enemy with a blunt weapon. Forgo your attack action, to attack dealing 1d4+str and on a failed Con dc 12+STR. Inflicting disadvantage on Attack and Saving Throws until the end of their turn.

Tells

You feel when people lie to you. You get Proficiency in Insight

Good Cop

Your experience as a Investigator lets you uncover hidden clues and tells other people might miss.

You get advantage on insight roles when questioning people

Freeze

LvL 15

As a bonus action you can once per long rest try to Shout at your enemies.  Designate up to 2 Enemies they have to Succeed a DC 16 Cha save or have their movement reduced to Zero

until your next turn

 

I Am The Law

Other Security  Workers(for a lack of a better word) Respect you. You get Advantage on Persuation other people in your line of work.

Your Presence and Dedication Intimidates your foes. People who suffered DMG from you get disadvantage on attack rolls against you until the start of your next turn.