Updated

THE HAGUE, Netherlands (AP) — A somber Queen Beatrix laid a white rose Thursday next to a new monument to seven spectators killed by an unemployed recluse who tried to slam his car into a bus carrying the Dutch royal family during last year's national day celebrations.

Other members of the royal family and relatives of the victims broke down in tears as they too laid roses next to the sculpture close to the scene of the April 30, 2009, attack in the central Dutch city of Apeldoorn.

The monument unveiled by Beatrix is a sculpture of a box full of balloons symbolizing vulnerability, festivities and mourning.

Security authorities stepped up precautions for the first "Queen's Day" festivities since Karst Tates plowed through a crowd and into a stone monument in Apeldoorn, killing himself and seven bystanders.

Beatrix and several members of her family looked on in horror from their open-topped bus, which was Tates' target. Footage of the scene, broadcast repeatedly over the next few days, stunned the nation.

The Apeldoorn attack "taught us we had to tighten things up" for Friday's celebration, said Jan Dalebout, the police chief responsible for Queen's Day security.

There were two arrests in the lead-up to Queen's Day, one of a 31-year-old man held on Wednesday "on suspicion of wanting to disturb the commemoration" in Apeldoorn. Separately, a 33-year-old man was arrested Thursday in the southern city of Middelburg "on suspicion of expressing threats against the Royal House."

Police did not give details of either case.

Hundreds of relatives of victims and other guests observed a moment of silence and white balloons drifted into the sky after the queen and Apeldoorn mayor Fred de Graaf drew back a white sheet covering the sculpture.

Relatives, many in tears, then laid white roses next to the monument. Princess Maxima, wife of Crown Prince Willem-Alexander, and other members of the royal family wept as they watched, before also laying white roses.

Police surrounded it with concrete barriers, installed extra security cameras and sealed mailboxes in nearby streets — a significant increase in security compared with last year, when Tates was able to speed through metal barriers.

His small, black car sent spectators flying like rag dolls before it missed the royal bus by meters and crashed into a needle-shaped stone monument.

Security will be tight Friday for the queen's visit to the southern province of Zeeland. Police have been given the power to pat down at random any member of the public, and residents near the queen's parade routes must remove garbage bins and other containers.

"We are responsible for the security of 45,000 people, so we have to be absolutely certain, and we've done that," said Koos Schouwenaar, mayor of Middelburg, one of two towns Beatrix is scheduled to visit.

"On the other hand, it has to be a party, so we have to avoid measures that will spoil the party," he added when announcing security earlier this year.

Vice Prime Minister Andre Rouvoet called Queen's Day 2009 "a black page in our history," but said he hoped this year's events would be "a happy day as we are used to."

In recent years, the Queen's Day holiday has heightened speculation that the 72-year-old monarch could announce her retirement. But even though Friday marks the 30th year of Beatrix's reign, there has been little talk about her abdication in favor of her eldest son.

While Beatrix remains popular among her 16 million subjects, Willem-Alexander's popularity has dipped this year amid criticism of his plan to build a holiday home on a remote Mozambique peninsula.

He was forced to abandon the project after media reports suggested developers were not keeping promises to help residents.

An investigation into last year's attack reported that the 38-year-old Tates confessed as he lay slumped and bleeding in his car that he intended to hit the royal family. He went into a coma shortly afterward and died of his injuries the following day.

Among his final words, Tates called Willem-Alexander a "fascist ... a racist," according to Tom Driessen of the national investigation bureau, which carried out the probe.