Dutch police said Tuesday that they have arrested another man on suspicion of involvement in the deadly tram shooting in Utrecht that left three people dead and three seriously wounded. Police said in a statement late Tuesday that the 40-year-old man was arrested in the afternoon by heavily armed officers in Utrecht.

They said the man "is suspected of involvement in the shooting. His role is under further investigation."

Police said two other men who were arrested following Monday's shooting have been released and are no longer considered suspects.

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The main suspect, Gokmen Tanis, 37, remains in custody. Dutch Justice Minister Ferd Grapperhaus said on Monday that the alleged shooter "was known" to justice authorities and had a criminal record, but would not elaborate.

Dutch justice officials confirmed Tuesday that the main suspect had been released from custody recently in a rape case that was due to go to court in July, BBC News reports. He was released early as part of a promise to cooperate with authorities.

Dutch prosecutors said a letter was found in the gunman's getaway car. That letter is one of the reasons a terrorist motive is being considered, BBC News points out.