Forensic teams are searching a house in Southsea as part of an investigation into the disappearance of a teenager 16 years ago.
Officers have travelled down from Scotland to search the former home of Peter Tobin, 60, who has been charged in connection with the disappearance of schoolgirl Vicky Hamilton.
The 15-year-old was last seen in 1991 after disappearing near Falkirk, Scotland.
Scottish detectives have been searching a house in Victoria Road North since Monday.
The house is believed to be where Tobin was living shortly after Vicky's disappearance, having moved down from Scotland.
The street is lined with Victorian terraced homes and yesterday a line of four unmarked police vehicles were parked outside the house. If any are driven away police cones replace the vehicles to ensure the parking space was not lost.
The police are keeping tight-lipped about what is happening behind the house's brown door, but residents have seen detectives and crime scene investigators, dressed head-to-toe in white coveralls coming and going from the house.
They have also spotted yellow boxes, lamps and tool boxes being carried into and out of the house by investigators from Lothian and Borders Police in Scotland.
One officer was seen to climb a ladder to check the guttering at the top of the house. There also appears to be plastic sheeting covering the hallway of the house.
Neighbour Adam Jeffrey, 42, said: 'I wondered what was happening and I asked the police but they're being really cagey and wouldn't tell me what was going on.'
Hampshire police says it cannot comment on the investigation as it is only assisting the Scottish force. However Portsmouth officers are standing guard by the front door of the property to ensure no unauthorised people enter.
Lothian and Borders police have released a one-line statement and are refusing to give any further comments.
The statement said: 'Officers investigating the disappearance of Vicky Hamilton are currently carrying out searches in the Southsea area of Hampshire.'
Looking into the backyard of the house neighbours can see officers coming and going from a big white tent that has been erected. At first residents thought police were digging up the garden but it now appears to be being used as a storage area for police equipment.
In June of this year police searched the house Tobin had shared with his ex wife Cathy in Robertson Avenue in Falside, Scotland. A specialist underwater team also searched nearby Boghead Nature Reserve.
Now their attentions have turn to the Southsea property as they try to piece together what happened in 1991.
Officers are yet to reveal how the search is being carried out, or how long they plan to be there, but the investigation at Tobin's former home in Scotland involved the family living there having to move out, all the furniture being removed and the house stripped to a bare shell.
Over two weeks police dug up the garden and removed the wallpaper and floorboards as they conducted a thorough search of the premises.
Looking at the ongoing search in Southsea, Norman Ngwenya, 39, of Victoria Road North, said: 'I can see into the garden but I can't tell what's going on. It's a bit worrying when you see lots of police outside.'
And student Apostolos Zourtoumadis, 24, added: 'I have seen men in white outfits going into the house. I've also seen them with cameras so they must be taking photos.
'I wondered if there'd been a murder or something and obviously was a bit worried.'
Vicky's family always feared the worst
Many people felt Vicky Hamilton had simply run away from home when she went missing 16 long years ago but her family always feared the worst.
The popular 15-year-old was known as bright, popular, and increasingly independent. Her relatives have long since accepted that is is almost certainly dead.
A huge search was launched for Vicky when she went missing on February 10, 1991 and officers were able to piece together a detailed picture of her movements until the trail suddenly went cold and nothing more was ever discovered.
Vicky, who lived in Redding, near Falkirk, Scotland, was returning by bus from Livingston, where she had spent the weekend with her sister.
She arrived at Bathgate, where Peter Tobin lived in 1991, at 5.25pm where she had to change buses.
She asked for directions to a bus stop where she planned to catch the 6.10pm service to home to Falkirk and at around 5.35pm, she stopped to buy a bag of chips.
She was seen to cross the road where she sat on a bench to eat, but has never been seen since.
Many assumed she had been drawn from the quiet town by the lure of big city life but but last November a special crime squad took another look at the missing persons case and began to treat it as a murder.
Her father Michael, a former bus driver, said: 'I don't believe Vicky ran away. She was a bright and bubbly teenager, tall for her age, who was starting to strike out on her own.
'I believe she was abducted and murdered. I hope the police will knock on my door some day soon and finally let me know what happened.
'There is somebody out there who knows something and knows where her body is, because people don't just disappear off the face of the earth.
'Somebody must know who did it, and they have been living with that for more than 15 years.'