Joint Base Lewis-McChord, Washington (CNN) -- For three weeks, security fears kept U.S. authorities from searching the Afghan village where an American soldier is accused of killing 16 Afghans, an Army investigator testified Wednesday. 

Local tempers were so high over the killings that it was too dangerous for the Americans to go, said Matthew Hoffman, a special agent with the Army Criminal Investigation Command. Negotiations with local leaders over the issue took 20 days -- and even then, the investigators were guarded by U.S. and Afghan troops and watched over by two U.S. helicopters, he said. 

"We were fully expecting to be attacked at any time," Hoffman said. "We didn't know how much time we had for our investigation." 

Hoffman's testimony came during an Article 32 hearing for Staff Sgt. Robert Bales, the soldier charged in the killings. The hearing at Joint Base Lewis-McChord, near Tacoma, Washington, will determine whether Bales will face trial for the deaths. 

Hoffman was the lead investigator in the case. His team collected blood samples, took photographs and found a number of 9mm shells at the site, but much of the evidence had been collected by Afghan troops the day after the March 11 killings, he said. 

The shooting spree near a small U.S. outpost in Afghanistan's Kandahar province last March strained already tense U.S.-Afghan relations and intensified a debate about whether to pull out American troops ahead of their planned 2014 withdrawal. 

Stunned friends recall good deeds of killing suspect 

Bales is charged with 16 counts of premeditated murder, six counts of attempted murder, seven counts of assault and the illicit use of alcohol and steroids. He could be sentenced to death if convicted. 
Who is the soldier charged in the killings? For how long did security concerns keep authorities from searching the Afghan village? How many was Bales accused of slaughtering? Why was it so dangerous for Americans to go in? Who is Matthew Hoffman? Where is the hearing going to be held? What did Hoffman's team collect? Who else had already collected evidence? How long did negotiations with local leaders take? What was the name of the hearing in which Hoffman testified? What province did the shootings take place near?
Joint Base Lewis-McChord For three weeks 16 They were expecting to be attacked any time lead investigator in the case near Tacoma, Washington blood samples, took photographs and found a number of 9mm shells at the site Afghan troops 20 days Article 32 hearing Kandahar