From the article quoted by Rick, here are the author's conclusions, taken verbatim:
In summary, it can be said that there is no evidence to support the idea of a premeditated massacre--particularly in view of the fact that over half the Americans in the field survived both the main shooting and the administration of coup de grâce shots by the Germans who entered the field. Nor is it reasonable to suggest that the main body of the Kampfgruppe mistook the men in the field for a fresh combat unit, or that there was a mass escape attempt that caused the Germans to open fire.
So how do we explain the shootings at the Baugnez crossroads on December 17, 1944? There seem to be only two reasonable explanations. The first is that it started in response to a specific escape attempt. Someone saw two or three Americans make the break described in a sworn statement made to Lieutenant Schumacker in October 1945; that person then opened fire and this in turn caused a commotion in the field as some of the prisoners tried to push through their comrades to the west. But this movement, and the fact that at least one and probably two Americans had by then escaped from the field, only exacerbated the situation, and other Germans in the vicinity then fired. Even if this theory is accepted, however, it in no way excuses the deliberate killing of wounded prisoners by those Germans who then entered the field.
The other explanation is that faced with the problem of what to do with so many prisoners, someone made a deliberate decision to shoot them. And it is significant that the majority of the American survivors spoke of a single German taking deliberate aim with his pistol and then firing two shots at the prisoners. The sheer number of Americans in the field and the fact that they were standing in a group meant that many were physically shielded by the bodies of their comrades. This explanation would then require that, after the main shooting, it was necessary to send soldiers into the field to finish off the survivors.
On May 16, 1946, Peiper and 70 members of his Kampfgruppe, plus his army commander, chief of staff and corps commander, were arraigned before a U.S. military court in the former concentration camp at Dachau, charged that they did "willfully, deliberately and wrongfully permit, encourage, aid, abet and participate in the killing, shooting, ill treatment, abuse and torture of members of the armed forces of the United States of America." The location chosen for the trial and the number of defendants was clearly significant, and it surprised no one when all the Germans were found guilty. The court of six American officers presided over by a brigadier general took an average of less than three minutes to consider each case. Forty-three of the defendants, including Peiper, Christ, Rumpf, Sievers and Sternebeck, were sentenced to death by hanging (Poetschke had been killed in March 1945), 22 to life imprisonment and the rest to between 10 and 20 years. "The Law of the Victors," as it has been called in postwar Germany, had prevailed. But none of the death sentences was ever carried out, and all the prisoners had been released by Christmas 1956. Peiper was the last to leave prison. Sadly, incomplete and rushed investigations, suspicions about the methods used to obtain confessions, and inadequate or flawed evidence ensured that guilty men escaped proper punishment, and there can be little doubt that some innocent men were punished during the trial. In the final analysis, justice itself became another casualty of the incident.