BOSTON — A state trooper is back on full duty after pepper-spraying an MMA fighter who participated in a Dec. 4 protest about the Michael Brown and Eric Garner grand jury decisions.

The trooper, whose name was never publicly released by police, was placed on restricted duty after police launched an investigation. But the probe is basically dead in the water because the pepper-spray victim won't respond to requests to be interviewed by authorities.

"The individual who posted a video of himself being pepper-sprayed by a state trooper during a demonstration in Boston on Dec. 4 has, to this point, neither made himself available for interview by department investigators nor filed a citizen's complaint with the State Police concerning the matter," Massachusetts State Police officials said Friday.

"Despite the department's efforts to visit the individual at his residence; leave contact information at a location he frequents; directly speak with a relative; and, finally, to send a written request for cooperation via certified mail to his residence, the department's efforts have gone unanswered," police officials said.

The pepper-spray episode happened on a Boston street near an I-93 highway ramp during protests against alleged police brutality and racial profiling. The demonstrations were triggered by recent grand jury decisions not to file criminal charges against the Missouri and New York officers involved in the deaths of unarmed men during confrontations with police.

Kin Moy, the Cambridge man who was pepper-sprayed while shooting the Boston protest video, told multiple media outlets that he planned to reach out to the ACLU before speaking with police. But apparently Moy, a Mixed Martial Arts fighter who's also known as Kin "Kong" Moy, has yet to speak with law enforcement officials about being pepper-sprayed on Dec. 4.

However, he did discuss the incident with Mass-MMA.com. Excerpts of that Dec. 8 interview appear below:

Meanwhile, State Police officials say they've "consistently expressed an interest in ... (Moy's) version of the events, as well as viewing any additional video he may have from the incident." But, "absent his cooperation," police said, "a fair and complete assessment of the incident remains incomplete."

Authorities have declined to publicly identify Moy as the protester who was pepper-sprayed. The State Police internal investigation is ongoing.

Moy, a top-ranked bantamweight MMA fighter in New England, received at least two blasts of pepper spray to the face from the trooper, who ordered him and others to move along at the Boston protest. "Whooh! That hurt! " Moy is heard saying in the video.

Below is a rough audio transcript of the video: