A man has been arrested on suspicion of daubing "Lee Rigby's killers should hang" on the RAF Bomber Command War Memorial in central London.
A 20-year-old was held at his home in Manchester last Tuesday on suspicion of an act of criminal damage at the memorial in Park Lane on June 5, Scotland Yard said.
The RAF Bomber Command War Memorial, which was created to remember the thousands of RAF crew who lost their lives in the Second World War, was vandalised twice in just over a week following the murder of Fusilier Lee Rigby in Woolwich, south east London, on May 22.
In the first incident on May 27, the word "Islam" was scrawled across the monument.
Red graffiti was also found on the Animals in War Memorial in Hyde Park, which honours animals that have served and died for the British military forces.
After the second attack on the Bomber Command Memorial, Crimestoppers said it was offering a reward for information leading to the arrest and conviction of those responsible for vandalising the memorials.
The RAF Benevolent Fund released CCTV footage which appears to capture the moment it was first attacked.
It shows what looks like someone spraying it.
The person stops a few times as traffic passes and looks around a lot before eventually moving out of the shot.
In a separate CCTV clip from a camera pointing towards the centrepiece of the memorial, a person is captured walking around the statue and looking up at it.
The Bomber Command Memorial remembers the sacrifice and bravery of the 55,573 RAF crew who lost their lives in the Second World War and was unveiled by the Queen last summer.
The Animals in War monument cost £2 million to build and was unveiled by the Princess Royal in November 2004 - the 90th anniversary of the start of the First World War.
Anyone with information about the acts of vandalism can contact Crimestoppers anonymously on 0800 555 111.