At this point I doubt we'll ever know for sure if he wrote the infamous newsletters or not.
Newsletters published in the late 80s to early 90s under his name contained racist content. For example:
Regardless of what the media tell us, most white Americans are not going to believe that they are at fault for what blacks have done to cities across America. The professional blacks may have cowed the elites, but good sense survives at the grass roots. Many more are going to have difficultly avoiding the belief that our country is being destroyed by a group of actual and potential terrorists -- and they can be identified by the color of their skin. This conclusion may not be entirely fair, but it is, for many, entirely unavoidable.
Indeed, it is shocking to consider the uniformity of opinion among blacks in this country. Opinion polls consistently show that only about 5% of blacks have sensible political opinions, i.e. support the free market, individual liberty, and the end of welfare and affirmative action…. Given the inefficiencies of what D.C. laughingly calls the “criminal justice system,” I think we can safely assume that 95% of the black males in that city are semi-criminal or entirely criminal.
If similar in-depth studies were conducted in other major cities, who doubts that similar results would be produced? We are constantly told that it is evil to be afraid of black men, but it is hardly irrational. Black men commit murders, rapes, robberies, muggings, and burglaries all out of proportion to their numbers.
When they were brought up during his 1996 election campaign, he said they were being taken out of context and were based on the situation and statistics at the time they were written.
In 2001 he denied writing them, and said he previously hadn't because it would have confused the voters, and because he took responsibility for them as they were published under his name.
There are people who claim he wrote them, people who claim he didn't write them but did proof and approve them, and people who claim he had nothing to do with them. One newsletter refers to Paul's hometown as 'my hometown', but as said there's no way of knowing if he was actually responsible.