Marini's career was marked by his long period of service in the American army, where he gained notoriety for his achievements in field missions and leadership tactics. After completing his service, he joined a certain police department's SWAT team, where he met and worked with Barry Burton, serving as his law enforcement mentor.
Later, Marini was scouted by Raccoon City-based private companies in 1996 as part of the "Bright Raccoon 21"'s initiative in founding a privately funded police special forces unit - the Special Tactics and Rescue Service. A former soldier with commendable survival skills, he was the popular choice to lead the department as Captain. Due to the insistence of Umbrella USA, the primary funder, this position instead went to retired US Army officer Dr. Albert Wesker. Both were given the rank of Police Captain and assigned their own individual teams, with Wesker given seniority over the division.
Arklay Mountains Investigation
In July 1998, the Raccoon Police Department reached an impasse in their investigation of a series of brutal cannibalistic murders in the outskirts of Raccoon City, and transferred the case over to S.T.A.R.S. from its detective division. On the night of 23 July, Marini led Bravo Team on a Bell UH-1 Iroquois and flew out into a section of the Arklay Mountains several miles northwest of the city, where they suspected the assailants were based. Flying overheard, the helicopter suffered an unexpected engine failure, and they were left stranded in Raccoon Forest.[notes 2] While securing the immediate area, they found the wreckage of a Marine MP vehicle with two dead Marine occupants. Finding documentation indicating they were transporting a Marine war criminal for execution, he ordered the team to prioritise hunting down the fugitive before continuing with their mission.
After an encounter in the woods with Zombies and vicious mutant dogs, most of the team escaped into the Spencer Mansion, a large estate built on behalf of the Umbrella Pharmaceuticals CEO Dr. Oswell E. Spencer. Per standard S.T.A.R.S. procedure, they split up to secure the mansion. During his own search he discovered the entrance to a subway system, used for transporting personnel covertly. Following the tunnel, he reached another facility, NEST, where he found Bravo Team's medic, Rebecca Chambers. Chambers herself had found the criminal, 2Lt. Billy Coen, but they had been separated for some time. Against his better judgment, he allowed her to remain at the facility to look for him, while he returned to the mansion to find his teammates.
Over the course of 24 July, still trapped in the mountains, Marini's investigation of the site uncovered evidence implicating Umbrella Pharmaceuticals in the spate of murders, having developed a biological weapon which leaked out from their secret lab beneath the mansion itself. Furthermore, he found evidence suggesting an agent under their employ was a S.T.A.R.S. member, sent out to the mansion with orders to betray the team as part of a cover-up. Whether he was able to determine who this individual was, however, is not clarified.
While searching the underground caverns beneath the courtyard, Marini was injured, possibly by a B.O.W. While trapped in the caves, he was discovered by members of Alpha Team, who had been sent out to provide assistance. He was shot soon after by Wesker, who was keeping tabs on his officers and found Marini. His dying words were a warning about a traitor and "Umbrella".