Daniel Boulton, 30, admits the manslaughter of his former girlfriend Bethany Vincent and her nine-year-old Darren Henson but denies their murder.
Ms Vincent and Darren, known to his family as DJ, were both found stabbed to death at their home in High Holme Road, Louth, shortly after 8pm on May 31 last year.
The prosecution allege Boulton carried out the brutal stabbings after walking 28 miles from his hostel in Skegness.
A jury at Lincoln Crown Court heard Boulton took a coastal route from Skegness to Mablethorpe and was seen at a car boot sale in Saltfleetby where he bought a yellow toy digger.
There were further sightings of Boulton walking along the B1200 near the village of Stewton and on St Bernards Avenue and Newbridge Hill after he entered Louth.
CCTV footage showed Boulton inside a Co-op store near High Holme Road at 1.45pm on May 31, and then at a Subway takeaway 20 minutes later.
The jury were also shown CCTV footage of Ms Vincent and DJ inside the same Co-op store at 5.13pm and then walking home.
At the same time Boulton was sat outside the HSBC bank in Louth Market Place.
The prosecution allege Boulton sent Miss Vincent a series of messages, which then halted for an hour.
Boulton, of Alexandra Road, Skegness, denies two charges of murder on May 31.
The trial continues.