Diddy Trial Highlights From First Day of Witness Testimony

The first day of witness testimony in Diddy's sex trafficking trial is in the books ... and TMZ is recapping all the notable moments from a busy day in court.

After the full jury pool for the federal criminal trial was selected Monday morning -- 12 jurors and 6 alternates -- the prosecution came out swinging in their opening statement, claiming Diddy made a sex worker urinate in Cassie's mouth during a "freak off" sex party.

The feds allege Diddy forced Cassie and another woman to participate in "freak offs" with male sex workers ... and they also claimed Diddy got violent with the women and sexually assaulted his former assistant.

Diddy's defense argued that the sex was totally consensual and the relationships were voluntary and beneficial for the women ... telling jurors not to judge him for his sexual preferences.

The first witness was a security guard from the Los Angeles hotel where Diddy was seen on surveillance video beating Cassie ... and he testified that Diddy tried to bribe him to keep quiet, though Diddy's defense countered that Diddy was only offering money because a vase was broken in the incident.

The second witness was a male sex worker who says Diddy directed the "freak offs" and masturbated while watching him have sex with Cassie, who paid for his services. He testified Diddy told him to pee in Cassie's mouth and says Diddy once got upset by a lack of baby oil being used. His testimony will continue tomorrow and Cassie is expected to take the stand as the trial moves forward.

Diddy's three daughters left the courtroom when the male sex worker gave his graphic testimony ... and during a break they were spotted chatting it up with Diddy's mom, Janice Combs, and eating chips.

Diddy had a Holy Bible with him and read some scriptures ... and he had a blank stare and was stoic during opening arguments.