The death of Lee Thompson Young was both shocking and sad. When it was discovered that Young took his own life, those close to him were surprised -- and so were authorities. No motive was been found yet, but now sources say they may know what was behind the 'Rizzoli + Isles' (and former 'The Famous Jett Jackson') star's suicide.

TMZ reports that Young never left a suicide note and had no telling entries in his diary. When authorities searched the actor's personal computer, they still found no clues as to what would have driven him to suicide, thus leaving an air of mystery around his death.

However, sources close to the star say he suffered from depression for years.

Members of Young's family came forward about the star's struggle with the mental illness, giving names of doctors who treated the actor. Authorities plan on interviewing Young's doctors to determine how severe his depression was.

In the meantime, Young's cast and crew at 'Rizzoli + Isles' paid a brief yet moving tribute to the star who was taken far too soon at just 29 years old. Our thoughts are with Young's loved ones during this heartbreaking time.

Watch the 'Rizzoli + Isles' Lee Thompson Young Tribute