Saudi authorities arrested a second man on Tuesday on suspicion of shooting dead two policemen and wounding two others in separate attacks in Riyadh, the interior ministry said.
The ministry said last week that the first suspect in the shootings in March and April was acting on instructions from the ISIL group in Syria, in the first alleged attack by the group inside the kingdom.
Authorities were alerted to the second man's hiding place in a desert area in Ramah province northwest of the capital Riyadh by a tip-off to an emergency phone number, the ministry said.
The suspect, Nawaf Sharif Samir Al Onaizi, opened fire on security forces who returned fire and wounded him, the ministry added.
ISIL last year called on followers in the kingdom to carry out attacks against Saudi authorities, Western expatriates and members of the Shi'ite Muslim minority there instead of traveling to Syria or Iraq to join the group.
The ministry had offered a bounty of 1 million riyals ($266,666) for the capture of Al Onaizi, whom it said had adopted a Moroccan accent and name to disguise his identity.
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