They have fingerprints linking one of the suspects to the murder scene. They have evidence that shows one of the suspects bought two knives over the Internet.
What investigators don't seem to have is a motive.
This not only leaves a grieving community with unanswered questions, it also places prosecutors, who must provide proof of premeditation in order to earn a first-degree murder conviction, in a less than ideal situation.
Yet it remains unclear whether the 'why' behind the January 27 murders of Half and Suzanne Zantop will be needed to convict alleged killers James Parker, 16, and Robert Tulloch, 17.
Criminal experts and prosecutors agree that such a case can be proved without a motive. But the lack of information to the public and yesterday's request of a special investigative grand jury leave questions lingering.
Armed with the evidence of the knife and fingerprints, and outwardly confident in their ongoing investigation, the Attorney General's office says it remains untroubled by the lack of motive.
"From our point of view, we don't need to establish one," Senior Assistant Attorney General Daniel Mullen told the Boston Herald last Thursday. "The motivation is not critical to proving our case."
What is critical, Mullen said, is that the evidence shows that the defendants committed the crime.
Affidavits in Tulloch's arrest, released Thursday, state that three weeks before the murders, Parker purchased two military-style knives off the Internet that specialists had identified as similar to those that could have been used in the slayings.
The other key piece of evidence in the Attorney General's arsenal: two fingerprints lifted from "unidentified items" at the crime scene that match those obtained from Parker right before he and Tulloch left Chelsea
The significance of the newest piece of evidence, the camping ax Parker may have had in his backpack at the time of his arrest, remains unclear, however. New Hampshire police obtained a warrant to search for "evidence of homicide, including but not limited to" the ax, which Parker had told them he had, and other "objects capable of inflicting injuries or death."
Yet, in what the Associated Press characterized as "an indication that there is much to learn about the murders," prosecutors have asked the courts to convene a special investigative grand jury, a move which implies that prosecutors feel they need more information to absolutely secure a conviction.
Calling the investigative grand jury just "one of the tools" available to the prosecutors' investigation, Senior Assistant Attorney General Kelly Ayotte said the decision to request the panel did not mean that prosecutors lacked sufficient evidence.
Questions of evidence aside, how likely is conviction if the motive is never uncovered?
"Very likely," according to Jack Levin, director of the Brudnick Center on Violence at Northeastern University in Boston. "Motivation is not a necessary condition for establishing the guilt or innocence of a defendant in a murder case," he explained.
Of course, knowing the motive would help the case against Parker and Tulloch, he said. And it would be better for the community to know what motivated the suspects, he added.
Levin said that he was "surprised" to learn that the motive had yet to be uncovered. From the conduct of the investigation, he said he assumed the authorities already knew the motive.
In Levin's own analysis, the Zantop case falls somewhere in between the "traditional" homicide, which occurs between people who know each other well, and one of the more recent and growing genre of "murders by strangers."
Where the victim and suspect have intimate connections, it is "not at all" difficult to determine motive, Levin explained. Two friends go into the bar, get into an argument, and one pulls a gun, he said as an example.
But in the case of the Zantops, there's so little evidence, that we can't even know for sure if the suspects knew their victims at all, he said.
This leaves plenty of room for speculation, of which the press seems to have taken full advantage. The theory that the crime stemmed from an illicit love affair has been retracted, and claims that investigators found Nazi literature in Tulloch's bedroom was also refuted by the Attorney General.
Levin said he leans towards the simplest explanation: Parker and Tulloch thought the Zantops were not at home when they showed up, or the knives "were simply to threaten the victims," and then, in the confrontation that ensued, the teens stabbed the two "out of panic."
But Levin readily admitted that the nature of the crime makes even this theory uncertain. "If they had used a gun, we wouldn't be speculating," he said. But "the intimate, in-your-face contact in the method of killing," does not seem to fit the crime by stranger scenario and suggests the murder was "somehow precipitated," he said.
"You can't get this angry ... with a stranger," he said.
The possibility Levin found most unlikely, however, was a sadistic motive. Perpetrators who murder for pleasure are typically white, middle age men, said Levin, who has studied sadistic murders and serial killers for the past 20 years.
"Its very hard to find a teenager who sadistically murders two people," he said. "So if it happened here, its almost unique."
