A 15-year-old schoolgirl from Tennessee who was thought to be in imminent danger when she disappeared with a 28-year-old man is now a homicide suspect.

Trinity Faith Quinn was named in an Amber Alert when she was reported missing by Rhea Central Elementary School on Monday (1 May). Amber Alert - short for "America's Missing: Broadcast Emergency Response" - is a child abduction alert system used when a child goes missing and is thought to be in danger.

Some of Quinn's clothes were missing and it is believed she was "manipulated" into running away with Daniel Clark, whom she had known her whole life and called "Uncle Dan".

During an attempted robbery at an Exxon gas station in Nashville on Tuesday, Clark reportedly shot and killed clerk John Daniel Stevens, 58, with Quinn in attendance.

Nashville Police Department said it appeared from CCTV footage that Quinn made no attempt to flee during the shooting, and shopped for items while Clark stood at the counter.

"It is this department's belief that (Quinn) had the opportunity to flee. We do not see any indication she was held against her will," said Metro Nashville PD spokesman Don Aaron, reported by Fox News.

The pair apparently escaped on foot, leaving their vehicle nearby. Tennessee Bureau of Investigation (TBI) have put Clark on their '10 Most Wanted' list.

On Wednesday morning, around the time of the Amber Alert saying Quinn was in "imminent danger of bodily harm or death," a dump-truck driver saw her standing at the side of the road two miles from the shooting and called police.

Quinn and Clark were found in bushes and surrendered to police without a struggle. Both are now in custody and suspected of murder.