• Law enforcement officials investigate around the scene of a shooting in a parking lot behind a dentist's office, Thursday, June 14, 2018, in Westminster, Colo. Photo: David Zalubowski, AP / Copyright 2018 The Associated Press. All rights reserved.
Photo: David Zalubowski, AP
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Law enforcement officials investigate around the scene of a shooting in a parking lot behind a dentist's office, Thursday, June 14, 2018, in Westminster, Colo.
Law enforcement officials investigate around the scene of a shooting in a parking lot behind a dentist's office, Thursday, June 14, 2018, in Westminster, Colo.
Photo: David Zalubowski, AP
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Law enforcement officials investigate the scene of a shooting in a parking lot behind Colorado's dentist's office. Thursday, June 14, 2018, in Westminster, Colo.
Law enforcement officials investigate the scene of a shooting in a parking lot behind Colorado's dentist's office. Thursday, June 14, 2018, in Westminster, Colo.
Photo: David Zalubowski, AP
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Law enforcement officials investigate the scene of a shooting in a parking lot behind a dental clinic, Thursday, June 14, 2018, in Westminster, Colo.
Law enforcement officials investigate the scene of a shooting in a parking lot behind a dental clinic, Thursday, June 14, 2018, in Westminster, Colo.
Photo: David Zalubowski, AP
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Law enforcement officials investigate the scene of a shooting in a parking lot behind a dentist's office, Thursday, June 14, 2018, in Westminster, Colo.
Law enforcement officials investigate the scene of a shooting in a parking lot behind a dentist's office, Thursday, June 14, 2018, in Westminster, Colo.
Photo: David Zalubowski, AP
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Law enforcement officials escort a man away from the front door of a dental clinic as police investigate the scene of a shooting in a parking lot behind the clinic, Thursday, June 14, 2018, in Westminster, Colo. less
Law enforcement officials escort a man away from the front door of a dental clinic as police investigate the scene of a shooting in a parking lot behind the clinic, Thursday, June 14, 2018, in Westminster, ... more
Photo: David Zalubowski, AP
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Law enforcement officials investigate the scene of a shooting in a parking lot behind a dentist's office, Thursday, June 14, 2018, in Westminster, Colo.
Law enforcement officials investigate the scene of a shooting in a parking lot behind a dentist's office, Thursday, June 14, 2018, in Westminster, Colo.
Photo: David Zalubowski, AP
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WESTMINSTER, Colo. (AP) — A 23-year-old man has been arrested on suspicion of murder in a shooting that killed a boy and left three others wounded outside a suburban Denver dental office.

The boy's mother and brother suffered life-threatening injuries Thursday afternoon. A man not related to the family also was shot in the parking lot in the city of Westminster but was less seriously wounded.

The suspect was captured about three hours after the shooting.

The Denver Post reports that he was booked into jail Friday on suspicion of first-degree murder and three counts of first-degree assault.

Officers say there is no relationship between the gunman and the victims and have not released a motive for the shooting.

Police didn't release the any of their identities.