SAN DIEGO -- A trainer accused of opening fire at a Vista boxing club after being barred from the gym, killing another trainer and wounding two others, pleaded not guilty Thursday and will stand trial Jan. 11.

Mark Anthony Diaz, 50, is charged with murder, attempted murder, assault with a firearm and making a threat. He faces 75 years to life in prison if convicted.

Diaz allegedly killed 52-year-old Hector Gil and wounded 21-year-old boxer Ricardo Gutierrez and trainer Peter Moreno at Pacific Coast Boxing the night of April 7.

Trainer Albert Gamez testified during a preliminary hearing last month that Gil told him in March that Diaz was upset with Gil because Gutierrez -- who had just turned professional -- switched from Diaz to Gil as his trainer.

Gamez said Gil had him listen to threatening voice mails from Diaz.

A temporary restraining order was obtained in February, seeking to keep the defendant away from Pacific Coast Boxing, prosecutors said.

Diaz had recently been fired from the club, gym owner Ari Soltani said.

Gutierrez, now 22, testified that Gil was "scared" and "upset" after being threatened by Diaz.

On the voice mails, Diaz threatened to harm the victim if Gil didn't settle their differences, Gutierrez testified.

Gutierrez said Diaz sued him for breach of contract and they settled for $1,500.

The boxer said he had just finished a training session with Gil the night of the shooting when he heard what he thought was a firecracker.

Gutierrez said he realized the pops were gunshots and ran toward a television and felt a sharp pain in his leg. As he ran, the boxer said he saw the silhouette of the shooter, who was wearing a black sweatshirt.

The boxer said the shooter aimed at him and fired five shots, with two whizzing by his head.

The boxer said he didn't realize anyone else had been shot until he saw Gil -- who had been sitting next to him in the ring when the shots rang out -- bleeding.

Moreno testified that the bullet that went through Gil hit him in the left shoulder.

Gil's son, Hector Gil Jr., said he ran toward the gym door when the shots ended.

He testified that he started to chase the gunman, but stopped when someone turned off the lights.

Gil Jr. said the suspect was wearing a sweatshirt with a distinctive "T" logo on the back. A sweatshirt matching that description was recovered during a search of Diaz's home, said Deputy District Attorney Patrick Espinoza.

Gunshot residue also was found on the truck Diaz drove, the prosecutor said.