Prosecutors say 16-year-old Arthur Alston pleaded guilty as an adult Thursday to third-degree murder and faces a maximum sentence of 20 to 40 years. Alston admits he threw the first punch.
His bail has been revoked since his arrest for allegedly punching someone at an alternative school in April.
One of four other teens charged in Conroy's death has also pleaded guilty to third-degree murder.
The 36-year-old Conroy lived in Philadelphia. The attack occurred in the afternoon on a concourse near City Hall.
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