The sole survivor of a deadly Long Island ambush by MS-13 was a member of the vicious gang — and went home to sleep after his four pals were butchered, defense lawyers said in court Tuesday.

Elmer Alexander Arteaga Ruiz, the key witness in the federal murder trial of alleged slay conspirator Leniz “Little Devil” Escobar, said under cross-examination that he never bothered to call cops or notify anyone right after he fled the 2017 massacre in a Central Islip park — adding that he was unaware everyone else with him was being fatally bludgeoned.

“After you escaped, you didn’t know if your friends were injured or neeed help?” asked defense lawyer Jesse Siegel.

“I didn’t know aything about them,” Ruiz replied.”You went home?” Siegel said.

“Yes,” Ruiz answered.

“To sleep?” Siegel said.

Ruiz responded, “Well, that perhaps may sound cowardly, but my mind was tormented, and all I wanted to do was go to bed and be home safe.”

He told Siegel he went to work at his landscaping job the next day — and a police witness has said Ruiz later led cops to the grisly scene that day.

Siegel also claimed in court Tuesday that Ruiz admitted to a cop he was an MS-13 member less than a month before the massacre that killed four young men.

In a bizarre courtroom exchange, Ruiz, 22, denied he ever told the cop he was a member during his March 15, 2017, marijuana bust — although the conversation is referred to in a police report.

“[The officer] asked you a lot of questions about your MS-13 affiliation,” Siegel said to Ruiz.

Ruiz responded, “I’ll be candid.

“[The cop] said, ‘Donald Trump doesn’t want you guys here, so I’m going to do whatever I have to do to get you out of here.’ “

Then-President Trump traveled to Long Island in July 2017 to rail against street gangs, specifically ultra-violent MS-13, noting the quadruple murder of Ruiz’s buddies a few months before.

Siegel said, “[The officer] asked you about MS-13?”

Ruiz replied, “No, the only thing he said to me was about Donald Trump.

“[Ambush victim] Michael [Lopez] could understand him, and he told me,” said Ruiz, indicating Lopez helped translate the cop’s comments from English to Spanish for him.

But Siegel introduced a Facebook Messenger exchange between Ruiz and some of the eventual victims of the April 11, 2017, attack, instructing them how to join MS-13.

“I’m down,” ambush victim Jorge Tigre wrote at one point. “I’ll do it.”

Ruiz identified himself during the online exchange as “Alexander,” followed by the MS-13 hand sign and the number 13.

Escobar, 22, an MS-13 hanger-on, is accused of luring Ruiz and his friends to their deaths to curry favor with the gang.

Nicknamed “Diablita,” Escobar smirked in an eerie police mug shot and giggled and joked with a paralegal in court Tuesday.

Her smile disappeared when prosecutors called her former boyfriend, Sergio Vladimir Segovia Pineda, one of the MS-13 killers, to testify.

Pineda, 23, whose nickname is “Temible” — Spanish for fearsome or one to be feared — is a cooperating witness who pleaded guilty to his role in the brutal slayings but has not been sentenced. 

“What was her role in the murders?” prosecutor Justina Geraci asked Pineda.

The young man replied, “She was one of those who helped convince the victims to come out to where we, the members of the gang, could kill them.”

“I was one of the participants,” he added during the chilling testimony. “I helped capture the victims and helped kill the victims.”

Despite Siegel’s contention that Ruiz was a member of MS-13, Pineda said the group was targeted because they were with a rival gang. 

In his testimony Monday, Ruiz said Escobar and another teen invited the witness and his friends to smoke marijuana at the park when they were set upon by “eight or nine” members of MS-13.

Ruiz fled, while his four pals were butchered with machetes, knives, an ax and even tree limbs, according to police.

Killed in the attack were Lopez, 20, Tigre, 18, and Jefferson Villalobos, 18, and 16-year-old Justin Llivicura, authorities said.

In other testimony Tuesday, Suffolk County Homicide Detective Jeffrey Bottari described the bloody carnage at the Long Island park.

“I’ve seen the unimaginable, or so I thought until I saw this,” Bottari said.

“This was by far one of the most horrific crime scenes we’ve ever handled,” he said. “It will be etched in my memory, as it will be for everyone after this. It was vicious. It was unimaginable.” 

He said investigators found “two very large blood pools,” along with “brain matter, pieces of human skull, skull fractures, drag marks, a trail of blood.

“Blood droplets on the fence where people had tried to escape,” he testified. “The bodies were dragged across the asphalt pathway.”

Escobar’s trial began Monday and is expected to last three to four weeks.