Hi Manyarna,
I moved to LA Linea from the UK last December on a permanent basis.
The reason I moved to this part of Spain is because I have friends living both in Gibraltar and La Linea.
As Sanchez 1 said, it does have its ' bad areas ', the boulevard across from the border is known locally as the Chicken Run ! as its where a lot of people have been mugged ( allegedly ) on their way back from Gibraltar in the early hours a little worse for wear !
The boulevard is a long stretch of new shops and bars which is a direct acess to the centre of La Linea, the part by the border has been completed but the other end is a building site as there's no more money left in the coffers to finish it !
I havent heard of any murders in LA Linea, but its like all places, be aware of your surroundings and you will be OK.
When I arrived here I stayed with my friends while I looked around at somewhere to rent, I tried a few estate agencies and found a flat after a week of looking.
Be aware that estate agents in Spain will charge the tenant a finders fee, I had to pay the equivalent of two weeks rent on top of the months rent and months deposit required by the landlord, and it all had to be paid in Euros !
Most agencies in Gibraltar make no charge to tenants but its wise to ask beforehand !
Santa Margherita is just outside of La Linea, it is a sprawling ' housing estate ' of cloned properties ( how people find their homes is beyond me, they all look the same ! ) and has no infrastructure, no bars, no shops, and poor road access once on the ' estate'
The Spanish authorities are trying to spruce up the immediate area across from the border with Gib. in an attempt to attract tourism, a new marina has been built and the long stretch of desolate beach to the left has been designated as a future park and walkway but will take an estimated four years to complete !
La Linea is not that bad, view it as ' work in progress ' !!