(CNN) Russians on Wednesday mourned the victims of a deadly shopping mall fire at memorial services across the country, releasing white balloons as flags fluttered at half-staff.

KEMEROVO, RUSSIA - MARCH 28, 2018: People mourning during the funeral of the Kemerovo shopping mall fire victims at the Kirovskoye cemetery. The 25 March 2018 fire at the Zimnyaya Vishnya [Winter Cherry] shopping centre in Prospekt Lenina Street killed at least 64, many of them children. Danil Aikin/TASS (Photo by Danil Aikin\TASS via Getty Images)

The blaze tore through the Winter Cherry mall in the Siberian city of Kemerovo on Sunday while it was packed with families on the first weekend of spring break. Authorities said 64 people died, 41 of them children.

Crowds in Vladivostok let go of balloons in memory of the Kemerovo shopping mall fire victims.

Grieving family members clutched flowers and photographs of young schoolchildren at the first funerals held for victims. Investigators have so far released 21 bodies for burial.

The chairman of Russia's federal investigating authority, the Investigative Committee, has indicated that a short circuit or bad wiring could be to blame for the blaze, state news agency RIA-Novosti reported . Investigators said the mall's fire exits were blocked and an alarm system turned off.

A shopping mall security guard, who investigators believe failed to turn on the fire alarm, was arrested on Wednesday, state news agency Tass reported. Earlier, he told press that the alarm was out of order. He is one of two arrested and three detained in connection with the case so far.

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