Managed to find some things!

Terpil was apparently a CIA staffer from 1965-1971, and in the 1970s became a "free-lance consultant, and dealer in arms and exotic bugging and terrorist bomb devices". He was arrested in 1979 on arms-traffic charges, and bragged about employing ex-special forces (11 others, total), who were traveling around and training guerrillas. It seems this first operated in Libya, in 1976, and he claimed to have trained a notorious terrorist named Carlos. Terpil also interpreted for Jimmy Carter's brother, when in 1979 Carter and his family attended Qaddafi's military parade in September. He lobbied for C-130 planes to be released to Qaddafi (Carter had blocked them on fears of Qaddafi's terrorist support) because Qaddafi was willing to pay, but the planes were still not released by 1981. He was freed on bail and allowed to demonstrate some of his wares to the US Secret Service Training Academy, where he was arrested again on charges of plotting a murder, and he fled after his arraignment (he pled not guilty) but was still at large by 1981. ^^1

This is all I managed to find on him at first. I was unsatisfied, obviously, so I went searching further. I managed to find an old "The Nation" magazine scanned, which I looked at. In it (Article called "The Case of the Flying Spies, citation below ^^2 ) is confirmed Terpil's previous position as a CIA employee, and we can see more information on his doings. While there is mentioned some possibility he was still colluding with the CIA, it's also mentioned that in 1977 he signed an agreement with Idi Amin's regime to supply them with $3.2 million of arms, explosives, and electronic surveillance equipment. Now, when Terpil loaded many of these things onto 707s, there were Israeli intelligence agents (reportedly) working to help load. Further, the CIA had informants close to Amin who would've and should've known about this, but no action was taken to stop Terpil, suggesting an undercover operation of some sort.

I also looked at another "The Nation" article in 1981, which asserted that Terpil had made deals with General Contreras of Chile ^^3, through his arms company (called "Inter-Technology Inc.", and also run by Edwin Wilson). This was quite a scandal, supposedly, in its time, and a huge issue given the possible connections with Amin and Qaddafi as well. The New York Times also ran a piece on what they called the Wilson-Terpin Libyan affair, but I can't access it at the moment (I'd have to go to a library that I can't go to at the moment). Did even more digging, and found more news articles on the subject. One, from "The Gazette", should provide some good information you'd like to know:

HAVANA - Convicted arms trafficker and former CIA agent Frank Terpil, one of the most notorious fugitives from U.S. justice, is under house arrest here pending investigation by Cuban authorities of his business practices on the island, sources said. Terpil's detention took place about three weeks ago, according to Canadian businessmen and other sources, who spoke on condition of anonymity. The Cuban government has made no public statement about the arrest...Canadian businessmen identified Terpil from photographs and because he repeated some familiar stories associated with him. ^^4

I wasn't content with that, though, so I found a September 1995 issue of "The Times" which also ran the story ^^5, and also a New York Times article that same September of 1995 that says that the Canadians were aware of Terpil's activities for quite some time (this was said by the spokesman for the Canadian Foreign Ministry) but that they didn't request his arrest (though businessmen in Cuba were complaining to them about Terpil). ^^6

The Times, in 1994 (a full year before the Cuba story), reported that there was an attempt by Qaddafi to trade Terpil in exchange for easing of sanctions for Lockerbie, which the US refused (all this according to an unnamed counterterrorism official) ^^7 . According to the Belfast Telegraph in 2014, this occurred:

The BBC tracked Terpil - who is wanted in the USA on charges of conspiracy to murder and selling plastic explosives to Libya - to his home in Havana where he talked openly about running a squad set up to wipe out Gaddafi's opponents abroad. ^^8

An October, 1995 New York Times article mentions once again that Terpil was indeed under house arrest in Havana, Cuba.

Other than the above, I don't have the ability to find much more. That should give you a fairly good idea of the narrative. This guy, a former CIA staffer turned arms-dealer turned terrorist-supplier turned-Libyan friend turned-Cuban businessman who was probably freed from house arrest sometime in the gap between 1995 and 2014, was quite a character!

^^1 The Libyan Menace John K. Cooley Foreign Policy, No. 42 (Spring, 1981), pp. 74-93

^^2 The Nation (New York, N.Y.) (1982) volume: 234 issue: 7 page: 193

^^3 The Nation (New York, N.Y.) (1981) volume: 233 issue: 18 page: 566

^^4 Cuba arrests CIA renegade terpil; canadian businessmen finger convicted arms trafficker. (1995, Sep 17). The Gazette.

^^5 Martin Fletcher, i. W. (1995, Sep 18). Cuba arrests fugitive weapons smuggler;frank terpil. The Times

^^6 Engelberg, S. (1995, Sep 18). Cuba holds ex-C.I.A. man U.S. sought for 15 years. New York Times.

^^7 Michael Theodoulou, i. N. (1994, Sep 02). Libya offers to trade CIA man;frank terpil. The Times.

^^8 Gordon, S. (2014, Feb 02). GADDAFI HOSTED IRA AT TERROR PARTIES. Belfast Telegraph.