The tragedy occurred when Gradoville -- who also played for the Bluejays from 2004-07 -- showed up to make a repair at a rental home he recently sold to a realty company, according to Omaha police.

Gradoville was shot multiple times outside the home ... and was found dead in the yard around 7:55 AM after cops responded to a report of gunshots.

43-year-old Ladell Thornton -- who is believed to have been renting the home -- was arrested on suspicion of first-degree murder, use of a weapon to commit a felony and possession of a firearm by a prohibited person.

The incident sparked sorrow from the University, prompting Creighton’s head baseball coach to say he was lucky to have known Gradoville since he was 17.

"Having Chris as a member of our staff over the last 18 months was tremendous because he was a such a great man and a great teammate," Ed Servais said.

"Whether you were a player, teammate or fellow staff member that needed a hand, Chris was one of the first guys to step forward."

Gradoville was a part of the 2007 Creighton team that won the school's first Missouri Valley Conference title ... and was later drafted by the Texas Rangers in the 24th-round of the 2007 MLB draft.

The president of the university, athletic director and other members of the athletic dept. released statements as well ... expressing their sadness over the loss.

"The Creighton community is absolutely devastated by the death of Chris Gradoville," the school said Thursday.

"Chris represented the very best of what it meant to be a Bluejay. He was an alumnus, former standout baseball player, and the volunteer director of baseball operations."