Suffolk prosecutors say he unknowingly tattooed a murder confession on Aaron Hernandez’s right arm.

Lawyers for Hernandez, a former New England Patriots star, adamantly deny that allegation.

Jurors on Friday heard from tattoo artist David Nelson, who took the stand in the double murder trial of Hernandez at Suffolk Superior Court in Boston.

Hernandez allegedly fired five shots from a 104-year-old revolver into a BMW at a stoplight in Boston’s South End on July 16, 2012, killing Daniel de Abreu and Safiro Furtado. Hernandez has pleaded not guilty to all charges.

Nelson testified he was working at Hermosa Ink in Hermosa Beach, Calif., when Hernandez and his fiancée, Shayanna Jenkins, walked in with their infant daughter in the spring of 2013.

He said Hernandez wanted “a front view of a pistol like it’s pointing at you,’’ as well as the “part of a revolver that holds bullets,’’ meaning the cylinder.

Hernandez specified that “God Forgives’’ should be written backwards so that he could “view it in [a] mirror,’’ Nelson testified.

Nelson said Hernandez directed him to leave one empty chamber in the cylinder, which he had chosen from a photo off the Internet.

Hernandez made the decisions about the features of the cylinder, Nelson said, though “I might have made suggestions to how it would be improved aesthetically.’’

All told, Nelson said, he etched the cylinder, two separate gun muzzles, and a shell casing with a wisp of smoke over it on Hernandez’s right arm, as well as the God Forgives tattoo.

He also drew “Blood. Sweat. Tears.’’ on Hernandez’s right hand. “Blood’’ and “tears’’ were red-colored, while “sweat’’ was drawn in black. Hernandez selected the colors, Nelson said.

With his first question on cross-examination, defense attorney Jose Baez appeared to mock the premise that the tattoos amounted to an admission of guilt.

“Did they really fly you from California to come in here and talk about tattoos?’’ Baez asked.

“Yes,’’ Nelson replied.

Baez also noted the word “men’’ tattooed backward on Hernandez’s arm near “God Forgives,’’ and prosecutors repeatedly objected when he referred to the “God Forgives Men tattoo.’’

He also jokingly asked Nelson if he had drawn gun tattoos on various celebrities, including Rihanna and Angelina Jolie. Nelson said he hadn’t.

Nelson also told Baez that Hernandez did not specify the number of chambers in the revolver or the caliber of the muzzle.

Nelson also told prosecutor Mark Lee that he and Hernandez had discussed another elaborate “gun tree’’ tattoo that he would get during another visit.

That tattoo would include a rifle positioned vertically as the “trunk’’ of the tree, with money bags hanging off smaller guns meant to be the “branches,’’ Nelson testified.

The phrase “Money Rules The World’’ would be etched above the tree, Nelson testified.

Hernandez, however, never came back to the shop for that tattoo, even after Nelson texted him to see if he was still wanted it.

Lee displayed part of that text correspondence on the courtroom monitors.

“Hey David here still want some ink today,’’ Nelson wrote. “Hit me up.’’

He later texted Hernandez, “Is this even your number homes?’’

Hernandez eventually responded, telling him “we’ll do it another day. . . . was away without a phone.’’

Lee also hammered the notion that Hernandez had called the shots on all the gun-related tattoos.

“Is there anything that you put on Mr. Hernandez’s body that he didn’t ask you to put on?’’ Lee asked.

“No,’’ Nelson said.

Travis Andersen can be reached at tandersen@globe.com.