AS I write this column I reflect on the fact that it is Good Friday, the 21st anniversary of the Belfast Agreement which helped bring peace to Ireland. Beyond the hope and expectations of many, the peace process involved a multi-party agreement between most of the political parties in Northern Ireland and an international agreement between the Irish and British governments.

Looking back, after two decades of transformation in Northern Ireland, it is essential to acknowledge all of the hard work and compromises that were made by political leaders on all sides. Decades of the Troubles involving thousands of deaths, tens of thousands of acts of violence, ethnic cleansing, walls separating communities and a hard border dividing an island largely came to an end.

READ MORE: ​Lyra McKee: Nicola Sturgeon joins tributes to journalist killed in Derry

Sadly, however, the murder of 29-year-old Lyra McKee on the Creggan estate in Derry shows that not all violence has come to an end. The talented journalist was covering rioting in Derry when she was shot dead during the unrest which the police are treating as “a terrorist incident”.

Lyra was a real star: a past journalist of the year, a top-30 under-30 in the media in Europe, a talented writer with a two-book deal, the first of which is to come out shortly. She can be seen on YouTube giving an inspirational TED Talk about her experiences overcoming hate and intolerance towards LGBT people like herself. If you haven’t seen it yet, please take a few minutes to have a look and share with your friends. She also wrote a moving letter to her 14-year-old self: “Kid, it’s going to be okay... it won’t always be like this. It’s going to get better... keep hanging on, kid. It’s worth it. I love you”.

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Reading all the tributes, I wish I had had the chance to meet Lyra. She was clearly amazing, she was inspirational and she had so much more to achieve in life, until someone took out a gun and ended her life. Minutes before the shooting, Lyra tweeted from the Creggan estate: “Derry tonight. Absolute madness”, and a photo of police Land Rovers, flames and rising smoke from the rioting.

There is no acceptable excuse from dissident Republicans or any others who back violence. They must stop. We also have to hope that this senseless death shakes the complacency at Westminster where Northern Ireland has been sorely neglected in recent years. The consequences of Brexit for peace in Ireland have been treated largely as an inconvenience.

READ MORE: Nancy Pelosi issues post-Brexit trade warning during Ireland visit

Brexiteer promises of technical solutions to avoid border checks in Ireland were exposed as a fiction this week with a leaked UK Home Office report. The memo to Her Majesty’s Revenue and Customs (HMRC) and the Treasury confirmed that any high-tech solution to the challenge of how to keep the Northern Ireland border open after Brexit is at least 10 years away. It went on to say that “the challenges of this work cannot be underestimated... no government worldwide currently controls different customs arrangements with no physical infrastructure at the border”.

Meanwhile, in public the UK Government claims it will be all right on the night, without providing any concrete details. This from a government whose most senior minister for Northern Ireland was so unqualified for the job that she admitted that “I didn’t understand things like when elections are fought, for example, in Northern Ireland – people who are nationalists don’t vote for Unionist parties and vice versa”.

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Thank goodness we heard some home truths this week from US congressional leader Nancy Pelosi, who has been in London, Dublin, Stormont and also visited the British border in Ireland. With the US as guarantor of the Northern Ireland peace process, her views and those of her high profile congressional delegation really matter. She warned that US trade talks with the UK could be endangered if the agreement was compromised. Not only does the UK have to satisfy the other 27 EU member states who are standing up for Ireland, but the United States as well.

This week we have been reminded that despite the Good Friday Agreement, not all of Northern Ireland’s problems have been solved and Brexit has the potential to enflame tensions and stoke violence. Like Scotland, Northern Ireland also voted to remain in the European Union. Like in Scotland’s case, Westminster has not taken the concerns of majority opinion in Northern Ireland seriously.

The death of star journalist and human rights campaigner Lyra McKee must be a wake-up call to everybody. The Good Friday Agreement is a precious thing and Brexit must not be allowed to endanger it. We must do everything to preserve peace and protect a bright future for all, which was the cause that mattered most of all to Lyra.