What were the Skripals’ movements on Sunday 4 March?

CCTV footage from a pub caught Sergei Skripal driving his daughter, Yulia, into Salisbury at 1.35pm. He parked his dark red BMW in the Sainsbury’s open-air car park at the Maltings shopping centre at 1.40pm. From there they went to the Mill pub and on to the restaurant Zizzi, arriving there at about 2.20pm and staying until 3.35pm.

Emergency services were called to the bench in the Maltings where the Skripals had fallen ill at 4.15pm. One of the few specific appeals counter-terrorism officers have made is for people who saw the Skripals between 1pm and 1.45pm – suggesting it is a crucial period. The public health concern around Zizzi and the Mill must mean that the pair had been hit by the time they arrived at those places – or were hit while there.

How was the nerve agent delivered?

The Met police have given no details. One intriguing fact they have confirmed is that Yulia Skripal arrived at Heathrow from Russia at 2.40pm on Saturday 3 March – 24 hours before she and her father fell ill. There have been claims that the nerve agent was planted in Yulia Skripal’s luggage. But there has also been speculation that the BMW is key: was the nerve agent smeared on a car door? Or were flowers that Skripal put on his wife’s grave laced with poison, as has also been suggested? A chemical weapons expert told the Guardian he believed the nerve agent, a novichok, was most likely in powder form and the means of delivery could have been as simple as a letter.

Has a Russian hit team been on the ground in Salisbury?

The city’s Tory MP, John Glen, seems to think so. He has expressed outrage that a “silent assassin” could attempt murder. There has been talk of a woman in a black face mask being spotted shortly before the attack. A rumour has also done the rounds that a Russian was found hiding in the roof of the Zizzi restaurant some weeks before the attack. None of these claims have been substantiated.

If Yulia Skripal did carry the novichok into the UK then there would have been no need for a hit team, but there is little doubt that Russian spies must have been in Salisbury to carry out reconnaissance. The notion that it might have been delivered by Yulia Skripal or even via the post is supported by the theory that DS Nick Bailey came into contact with the novichok not in the Maltings but at Sergei Skripal’s home.

How is the police investigation progressing?

The police say the investigation is dynamic and fast-paced. The scale and scope is unprecedented. About 500 detectives, police officers and staff are involved, supported by 200 military personnel. Add in the paramedics and firefighters, and about 1,000 members of the emergency services and military are involved. Approximately 20 cordons across two counties, Wiltshire and Dorset, have been set up.

Investigators have been returning to the scenes as more information and leads have emerged. But the police have not made any arrests – apart from a man who breached a cordon after a night out – and have not issued any appeals for suspects. It would be usual in a case of a double attempted murder for police to issue details such as CCTV footage of the victims. They have not even issued images of the Skripals – the only ones seen have been found and published by the media. One of the earliest images to emerge was of a couple – a man and woman – in Market Walk shortly before the Skripals collapsed, but police have not said if they are believed to be the Skripals or anyone else connected with the investigation. There are still many more questions about what happened than there are answers.