3:32 PM PT -- Dominican Republic police have released the mug shot of the man they say shot Big Papi, 25-year-old Rolfi Ferreira Cruz.

D.R. officials also announced they have now arrested SIX total people in connection with the attack on Ortiz ... and say there is at least 1 other suspect still on the run.

The man who allegedly shot David Ortiz has been arrested ... officials announced Wednesday -- saying the shooter, along with 5 other suspects, were paid 400,000 pesos to kill Big Papi.

As we previously reported, Ortiz was shot in the back on Sunday night as he was sitting in an outside patio area of a popular Dominican Republic nightclub.

D.R. cops say two young men drove up to the scene on a motorcycle ... when one of them got off to fire a single bullet into the Red Sox legend's lower back.

Cops say the guys tried to flee the scene on the bike afterward ... but when it fell to the pavement -- they tried to make a run for it on foot.

One of the guys -- the alleged shooter -- was able to escape ... but the other suspect, Eddy Vladimir Feliz Garcia, was beaten to a pulp on the scene by bystanders before he was handed over to cops.

Now, D.R. officials are saying they've caught the suspected shooter and arrested him ... and have also detained 3 additional people they say contributed to the ambush.

Officials say 6 total individuals were paid 400,000 pesos (the equivalent of $8K) to kill Ortiz in what they believe was a highly-orchestrated attack.

They say the ambush involved 2 vehicles and 1 motorcycle ... and announced 5 of the suspects are now in custody, but one remains at large.

A motive has yet to be determined.

During the press conference, officials also presented the gun they believe was used to shoot Ortiz.

Big Papi underwent surgery late Sunday night to repair the damage the bullet caused ... with surgeons saying they needed to remove his gallbladder and parts of his intestines.

David underwent a second procedure on Monday night after he returned back to Boston.

In a statement released Wednesday by Ortiz's wife, Tiffany Ortiz, she said, "His condition is guarded and he will remain in the ICU for the coming days, but he is making good progress towards recovery."