A US congressman has posted a Christmas picture of himself and what appears to be his family, smiling and posing with an assortment of guns, just days after four teenagers were killed in a shooting at a high school in Michigan. Thomas Massie of Kentucky tweeted: “Merry Christmas! ps. Santa, please bring ammo.” Ethan Crumbley, 15, faces charges of terrorism and murder after the deadliest school shooting in the US this year. His parents were arrested on Saturday in connection with the killing of Tate Myre, 16, Hana St Juliana, 14, and 17-year-olds Madisyn Baldwin and Justin Shilling at Oxford high school near Detroit. Six other students and a teacher were wounded in Tuesday’s shooting. Massie, who represents a solidly Republican district, posted the picture of himself and six others holding firearms resembling machine guns and semi-automatic weaponry, some of which are made to look almost identical to fully automatic weapons. Under US law, weapons such as machine guns are restricted to the military, law enforcement and civilians who have obtained special licenses for weapons made before May 1986. Jonathan Van Norman, a campaign manager for Massie, did not immediately reply to a request for comment via Twitter. The Democratic US Representative John Yarmuth condemned his fellow Kentuckian’s post. “I’m old enough to remember Republicans screaming that it was insensitive to try to protect people from gun violence after a tragedy,” Yarmuth tweeted, apparently referring to calls for gun control laws. “I promise not everyone in Kentucky is an insensitive asshole,” he added. The shooting in Oxford, Michigan, was the latest in a string of such incidents that have prompted fierce debates over school safety, gun control and gun rights. A judge in Michigan set bail at $500,000 (£378,000) each for Ethan’s parents, after authorities arrested the couple on Saturday after a manhunt. Appearing by videolink from jail for their arraignment, James and Jennifer Crumbley both pleaded not guilty to four counts of involuntary manslaughter. The Oakland County prosecutor Karen McDonald told the hearing the Crumbleys withdrew $4,000 from an ATM while authorities were searching for them and remained a flight risk. “These are not people that we can be assured will return to court on their own,” McDonald said. Authorities began searching for the Crumbleys after prosecutors said on Friday that the couple would be charged with manslaughter in connection with the shooting. Prosecutors said the Crumbleys bought a handgun for their son as a Christmas present and then ignored warning signs including on the day of the shooting. The judge, Julie Nicholson, said on Saturday she had “some concern about the flight risk” posed by the couple after they did not appear for the Friday arraignment. The Crumbleys’ lawyers have said the couple never sought to evade authorities. “Our clients were absolutely going to turn themselves in,” one of the lawyers said at Saturday’s hearing. “It was just a matter of logistics.” Detroit’s chief of police, James White, told reporters on Saturday that the couple had been found hiding in a commercial building on the east side of the city. He said they had not broken into the building, but were let in by somebody. White said the couple’s vehicle had been outside the building. Four days before the shooting, Ethan accompanied his father to a gun shop, where James Crumbley bought a 9mm handgun, prosecutors said. Ethan posted photos of the gun on social media, writing: “Just got my new beauty today,” and adding a heart emoji. The next day his mother posted that the two of them were at a gun range “testing out his new Christmas present”, McDonald said. The prosecutor detailed a number of other warning signs that she said the parents failed to act on. On 21 November, a teacher found Ethan searching for ammunition online on his phone and alerted school officials, who left messages for his mother that went unreturned. His mother later texted him: “LOL, I’m not mad at you. You have to learn not to get caught.” On the morning of the shooting, a teacher discovered drawings by Ethan that depicted a handgun, a bullet, and a bleeding figure next to the words “blood everywhere”, “y life is useless”, and “the thoughts won’t stop – help me”. Ethan told school counsellors the drawings were for a video game he was designing, and that he wanted to pursue video game design as a career, according to a letter that the Oxford community schools superintendent, Tim Throne, sent the school community on Saturday. “At no time did counsellors believe the student might harm others based on his behaviour, responses and demeanour, which appeared calm,” Throne said. School officials summoned the Crumbleys and instructed them to get Ethan into counselling within 48 hours, McDonald said. She added that the parents resisted the idea of taking their son home, and did not search his backpack or ask him about the gun.