Can CID task a non-CID/MP soldier to assist with an investigation?

So I see none of my CID counter-parts have answered yet so I'll tell you what I know. First, for a little background on myself, I have worked some cases in the past with CID as a CI Special Agent in a field office (when I was with the 902nd--they were cases that involved alleged support to terrorism which is where CID and CI often cross paths). In any case, I did see actual MPs working in some CID field offices at this time in addition to plain clothes MP's conducting investigations, but these were exclusively MPI's (Military Police Investigators--MP's that have been to MPI school and have a V5 ASI I believe. They handle various cases that CID can't get to--mostly misdemeanors requiring follow-up investigation if I'm not mistaken). I have not personally seen but have heard from some of my MP friends that they have also assisted CID in the past but nothing too in-depth. My understanding is that regular every day run-of-the-mill MP's have very limited investigative training. However, based on what I said above I wouldn't put it past the realm of possibility. With that, the person you describe does not sound like he meets any of these requirements and may just be exaggerating or outright lying to look cool. But, without knowing more about him there is no way I could tell you for sure. I would take anything he says with a grain of salt based on what you are saying.

Gonna call BS on this one. I can see maybe using the member as a confidential informant but definitely not as an active investigator. That takes specialized training the average "beat cop" just doesn't receive.

Can't answer your question but I wanted to share a CID story from a long time ago. I think the statute of limitations has come and gone. ;-)

In 1973 I was part of a small detachment of MP's from Company A, 385th MP Bn, 15th MP Brigade, in Neu Ulm, Germany. There were maybe 20 of us in the detachment. I was the senior patrolman on day shift one day and was in a restricted area at an ammo dump, 4-wheeling in my new M151A2. Wasn't supposed to be there, but there were some good hills to climb and there was nothing going on that day.

I was following the trail around the perimeter fence and was part way up one particularly steep incline when I spotted an OD green canvas satchel lying next to the fence. I backed the jeep down and walked back up to get it. Looked inside and didn't know what it was so I figured I had better take it to the MP station despite having to admit where I found it.

Turned it in to the desk sergeant and he went ballistic, yelling for our MPI agent. The MPI agent went ballistic and started yelling for our CID agent. The CID agent went ballistic and tried to give it back to me, telling me to put it back where I found it and not to say anything to anybody. Turns out it was a satchel of C-4 and nobody wanted to be responsible. I refused to take it back and they were still arguing over it when I left. No idea whatever happened to it.

SGT Dave Tracy I can see them asking SFs/MPs to assist in an investigation, but, recollecting my training through Security Forces, to actually take part in an undercover assignment, you would need to be part of CID/OSI, unless expressly authorized from your CoC.
The only way I can think to insert a regular member would be to get authorization from CoC, but CoC would keep said assignment private from member in order to keep the details secret so said member doesn't spill the beans.
I'm with you, though, that sounds a bit James Bond-y.

I have to echo the comments of CW4 Shaun Collins. We did, from time to time get non-MP soldiers attached to the local CID office in an OJT status, always with the purpose of eventually qualifying to apply to become a CID Agent. I saw CID Agents go undercover in specific, targeted units or on-base activities, with specific goals in mind. In all my years, I never heard of CID recruiting some random soldier and sending them undercover for anything.

I was contacted by CID that a Soldier in our Battalion was being utilized as an informant to gain additional information on an individual that was engaged in selling drugs to personal on our Army base. I asked how our Soldier was involved in this and the agent stated that our Soldier was a low level drug seller and they were trying to take down the network in Colorado Springs. So, I would answer Yes to your question.

Just to flesh it out a bit more since there is a character limit above, the tale is that for unknown reasons, he was selected by CID to report to a different unit (I think same post, but I don't remember all the details anymore) get in tight with those soldiers and report on some supposedly illegal activities. He had no prior knowledge of any crimes or knew any of the soldiers in that unit. He was basically a spy inserted into the unit and reporting back to CID.

Sounds too "spy novel" for me to accept at face value, but maybe I'm wrong.

Direct assignment, I do not believe so, for a temporary assignment because of special skills or knowledge, yes. They would have to go to your chain of command (Tradition and Courtesies for sure) and requests your assistance, Usually granted as far as I know because it is a rare thing. I have seen it happen once, but for further info I would direct this to one of our MP personnel for a more full answer (or to correct me and show that what I saw was a bolt out of the blue.)

the air force investigators have gotten into a lot of trouble for use of "special Informants"

The answer is yes, to a limited degree. I was a CID agent from 1978-1994. I have used mine detection teams from the engineers to search for buried weapons used in murders and attempted murders. Routinely, we used five unit members of the suspect as “fillers” in lineups. The standards require the fillers to be of the same gender and race as the suspect. It also requires the fillers to have the same physical build, complexion and of the same weight and height. If you refuse, I give you an order to stand in the lineup. If you refuse the order, you went in my report as a subject of refusing a direct order. The courts also have indicated that I could also order you to shave your mustache off, if there was no other filler in the unit which fit the clean shaven appearance of the suspect. There are other occasions where I woke up personnel sergeants in the middle of night to get the names of all newly arriving NCOs with a particular name when I was hot on the trail of a senior NCO who shot a lower ranking soldier in the head while in a German club. The importance of catching the perpetrator was more important than the SIDPERS NCO’s sleep. After explaining why we ask him to come in, he also saw the need for his expertise. With his help, I woke up every soldier with that last name and found the perpetrator. He waived his rights, confessed and took me to the area where he buried the gun. The mine detection team found the gun and it was confirmed at the crime lab as the weapon used in the attempted murder.