LOWELL — State police closed Interstate 495 for hours on Tuesday, as they cornered a silver pickup truck on the median in Lowell, as the driver was suspected of shooting an killed another man, who he knew, in an altercation at about 3:30 p.m. at the Shops at Highland Commons on the Hudson/Berlin line.

Both lanes of 495 were closed from about 4 p.m. to 7:30 p.m. creating a massive backlog of traffic in both directions during the evening rush hour.

Police say a witness from the Berlin plaza followed the suspect’s car on I-495 north and alerted police, who caught up with him, pinned him down to the median strip and engaged in a standoff for several hours. Eventually State Police armored vehicles moved in and rammed the pickup truck, and a drone was used to fly onto the truck to get a video picture of what was going on. They used a robot dog to bust out a side window, and then advanced to the truck, and found that the man had killed himself by a self-inflicted gunshot wound, according to Worcester Country District Attorny Joseph Early.

A section of the parking lot of Highlands Commons near the Fit Factory and Mooyah burger place at the plaza was cordoned off with police tape and police had two shade covers set up. A witness from the area said a person had been shot in the head and killed.

Early said first responders at first tried to save the man who had been shot several times in the Berlin plaza parking lot but that he died on the scene.

A worker at the Fit Factory said they heard  been shot and killed in front of the gym, but they had not been in the gym at all. “Some people saw something, but no one really knows what’s going on,” the person said.

Berlin Police posted on their Facebook page that they responded to the Highland Commons parking lot at 3:30 p.m. for a report of an assault in progress, and were told as they approached that shots had been fired. They said there was no ongoing threat to the community, but that they were investigating the incident along with the state police.

During the standoff, people were warned not to gather on the overpasses to I-495, as there was a firearm involved and they could be putting themselves at risk.

According to MassDOT, northbound traffic on I-495 is being diverted at Exit 89 (Route 3), while southbound traffic is being diverted at Exit 92 (Route 38). Temporary signs and message boards are being deployed to advise drivers to seek alternate routes, and those traveling through the area should expect delays.

Massachusetts State Police announced at 7:27 p.m. that the southbound side of Interstate 495 had reopened. And MassDOT announced just past 8 p.m. that one lane had reopened on 495 north, but two were still closed at that time. And at 9 p.m., Early said a second lane was open on 495 north, but one was still closed due to the investigation.