Friends and family of producer Johnny "J" Jackson are simply stunned that he died at age 39 over the weekend.

According to a source close to J and his family, he was serving a sentence in Los Angeles County Jail for DWI. The source confirmed reports that he died after apparently jumping to his death off an upper level at the jail. One jail spokesperson has not yet returned MTV News' phone calls, while another was trying to retrieve information on the incident.

Jackson, known in the music industry as "Johnny J," might not be as widely known as Swizz Beatz or Timbaland, but his stats are impressive. He produced about half of Tupac Shakur's All Eyez on Me double LP, including the hit "How Do U Want It."

"When I talked to him, he told me he sold over 100 million records," King Tech from "The Wake Up Show" said Monday (October 6). "He has a bunch of stuff. ... In my opinion, he needs to be put up there on legendary status with a Quincy Jones or Dr. Dre, because nobody knew he sold that many records. He was more of a low-key guy. He didn't go out there flashing his money, but when you go to his studio, you'd see 100 'Pac plaques. You'd be like, 'Man, you did all of these records?' "

J's last major interview was with Tech on "The Wake Up Show" four months ago, right before he went to jail. The producer told Tech and the listeners that he had around 30 Tupac records in his vaults that were unreleased and that he was part owner of all of 'Pac's recordings.

"We did six or seven a day," J said of the MC's schedule. "Depending on how the Hennessy was going, we turned it out."

"Tupac's real life was like a movie to me, and Johnny J was a big part of the score and soundtrack to that movie," L.A. lyricist and former Death Row artist Crooked I told MTV News. "The classic songs he produced for 'Pac will be with us forever -- us being the West Coast and the whole world. Real talk!"

King Tech said working so closely with Tupac and then losing him took its toll on J. "I think that always played in his psyche: 'My best friend, my partner, is gone.' I think that always affected dude," Tech said.

Tech also said J never worried about getting the recognition that some other producers have gotten, but he did stay on top of his business and was living well off of Tupac royalties alone. Before going to prison, Johnny J was working with local, unknown groups in L.A. such as the Hux and spearheading an album by Tatyana Ali from "The Fresh Prince of Bel Air."

Johnny J started off in music on a high note, co-producing one-hit wonder Candyman's debut album, Ain't No Shame in My Game, which spawned the commercial monster "Knock the Boots." A few years later, he started working with Tupac's group Thug Life, which eventually led to working on 'Pac's superstar solo material and posthumous albums.

"If we could have just 10 minutes to talk, I think the outcome could have been different," Tech said of his friend's demise. "Unbelievable. The dude was set for life. With the amount of hits he has out, once you read his biography, the amount of songs he had was insane. It is really strange. Everybody is confused out here. Everybody I talk to are like, 'What?' He wasn't broke, publishing was coming in, he had a wife, he had two kids and a big house. He had everything. He didn't need to go."

You can watch Johnny J's last interview with King Tech on "The Wake Up Show" Web site.